Effect of carbon tetrachloride (CCl4) sonochemistry on the size of active bubbles for the production of reactive oxygen and chlorine species in acoustic cavitation field

Abstract

It is known that the evaporation of carbon tetrachloride (CCl4) into the acoustic cavitation during water sonolysis results in the generation of many reactive species (e.g. chlorinated elements), probable reduction of bubble temperature and the scavenging of hydrogen atom by its reaction with CCl4. Consequently, the chemistry of bubbles (sono-activity) is completely modified, which means that the change of the active bubbles distribution is more plausible in the presence of CCl4. The present work gives the first study of the impacts of carbon tetrachloride on the size distribution of active bubbles as well as the optimum size for the maximal yielding of reactive oxygen species (ROS: ●OH, O, O3, HO2● and H2O2) and reactive chlorine species (RCS: ●CCl3, :CCl2, ●Cl, Cl2, HOCl). In addition, the extent of these effects (of carbon tetrachloride) was evaluated as function of the ultrasonic parameters, namely, ultrasound frequency and acoustic intensity. It has been shown that the optimum ambient bubble radius for the maximal production of ROS and RCS shifts towards higher values (~6–7 µm) when CCl4 concentration is greater than 0.02 mM (i.e. for a frequency of 300 kHz). However, for lower concentrations of CCl4 (<0.02 mM), this optimum exists at around 3.1 µm. As the acoustic intensity is raised, the range of active bubbles and the optimum size are increased, where this effect is more intense for CCl4 concentrations greater than ~0.01 mM. For higher frequencies, 875 and 1000 kHz, it has been demonstrated that the existence of CCl4 in the bulk liquid practically has no effect on the optimum size for the maximal yielding of oxidants.